The invention relates to a process and a device for the control of the electric braking of a direct current motor, in particular a traction motor.
The electric braking of traction motors equipped with current chopper controls has been carried out heretofore in two fashions, when it is desired to maintain the braking force at velocities lower than the rating of the traction motor.
In one prior arrangement for achieving electric braking, illustrated in FIG. 1, the inductor and the armature of the motor are in series, wherein the inductor may comprise a variable shunt, and a chopper is mounted in parallel between the load and the motor so as to make control of the load possible, even when--in the special case when the load is a source of power--the voltage or electromotive force of the motor, when it functions as a generator, is less than that of the power source. This layout has disadvantages related to the instability of the generator series excited winding, where an increase in the current in the inductor tends to increase the voltage on the terminals of the assembly.
In another prior arrangement for achieving electric braking, illustrated in FIG. 2, the traction motor functions as a generator, discharging onto the grid or on any particular load. The excitation of this generator is controlled by a chopper-inductor assembly connected in parallel with the terminals of the generator. Such a system permits control of the excitation field of the motor by means of the chopper only. In cases of operation wherein the current in the inductor must be weak compared to the current of the armature, this process becomes difficult to apply, because the chopper must operate at a very low cyclic rate, causing certain instability problems to appear.
One of the objects of the invention is to eliminate the disadvantages of the known devices by providing the electric braking controls of said motors with an increased flexibility.
A further object of the invention is to insure with simple means the control of the electric braking of traction motors both in the case of rheostatic braking and of regenerative braking.